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Really long eq explaination

EQ's are used on main speakers for two very different reasons.
1. Correcting uneven frequency response in the speaker system.
2. To avoid exciting troublesome frequencies in a room.

In fact due to these different requirements it is not uncommon to see two eq's used in series on a single speaker system, one is used to clean up the frequency response of the speaker (and is never changed again after being setup), and the second is used to compensate for room effects. I would only consider using 31 band eq's since the 15 band eq's are not selective enough. Best of all is to use parametric eq's, but these can be tricky to setup.

Smoothing out the roughness in your speaker systems frequency response, especially around the crossover frequencies will help eliminate feedback problems and will also make the speaker sound a lot better. What you are trying to do is tame the bigger spikes and make the response generally smoother, not flat. It isn't possible (or even desirable) to make a speaker system ruler flat, you just don't want any big spikes in the response. You would expect that the crossover in your speakers would take care of this issue, but the reality is that lower cost speakers don't pay as much attention to this so you usually have to do some cleanup. Plus as soon as you add a subwoofer to your system you are totally on your own when it comes to getting a smooth response.

Note: Real speakers (as apposed to marketing fluff) roll off at both the low and the high ends (this is what the smile eq is trying to compensate for), but the reality is if you boost these frequencies enough to make the response flat you are going to have a harsh sounding high end and your system will probably clip on low notes. Not a good situation at all. Remember cut only, never boost with an eq.

To eq a system properly requires a certain amount of test gear. The best solution is to use either a TEF or a SMAART audio analyzer system. These will let you see the actual output of the speaker and eliminate reflections from the room. These are big buck solutions and take training to use. If you can find someone who has one of these it would be worth it to pay them to setup your eq for you (and then put a locking cover over your eq so no one, including you, will mess it up).

Most pro audio shops will have an RTA which has a set of level LED's (like a vu meter) for each frequency slider on your eq. The problem with an RTA is that it doesn't distinguish between the direct sound from the speaker and the reflections from the room. To sucessfully use an RTA to eq a speaker you really need to do it outside, in a large flat area (no nearby buildings).

Alternatively you could buy a test CD that has test tones on it and a Rat-Shack sound level meter and adjust it yourself. Don't worry that much over 10 KHz. The low-mid and midrange is where your system really needs to shine.

The issue of problem frequencies in a room is caused the fact that every room resonates at certain frequencies (determined by the physical dimensions of the room). This is the reason why certain notes will sound really boomy in some rooms and not in others. The idea is to identify the resonant frequency of the room and then reduce the amount of energy you put into the room at that frequency.

You can do this pretty easily with an RTA. Play pink noise through your system at about 95 dB (make sure the room is empty or people will complain) and then mute the pink noise. Watch the RTA display to see which band in the low-mids (under 800 Hz) takes the longest to drop. This is the fundemental resonant frequency of the room, do it a couple of times until you are sure you have the right band then cut that frequency 6 db on your eq. Do this again only this time looking in the high-midrange band (1000 - 8000 Hz), and this time only cut by 3 dB. Do this once or twice more looking for other problem frequencies (only cutting by 2 to 3 dB) throughout the entire audio range. Avoid doing this too much (especially in the area between 1 to 4 KHz) or your vocals will start sounding thin.

After you are done listen to a music CD that you know well. Does it sound OK? If not reduce your adjustments (put them closer to flat) until you are happy with the sound.

P.S. A round room is the worse possible audio space followed closely by a square room. If you are forced to perform in these kinds of spaces, spend as much time beforehand as possible figuring out the problems in these rooms.

Phil


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